The temperature at which a carbonated soft drink turns to a solid is consistently lower than the \(32^\circ\text{F}\) (\(0^\circ\text{C}\)) freezing point of pure water. This difference results from the various dissolved ingredients, which interfere with the natural crystallization process of water molecules. Most regular sodas begin to freeze in the range of \(30^\circ\text{F}\) to \(31^\circ\text{F}\) (about \(-1^\circ\text{C}\) to \(-0.5^\circ\text{C}\)), though the exact point varies by brand and sugar content.
How Dissolved Solids Lower the Freezing Point
The primary factor determining a soda’s freezing temperature is Freezing Point Depression. This colligative property dictates that adding a solute (dissolved particle) to a solvent lowers the solvent’s freezing temperature. In soda, the solvent is water, and the main solute is sugar, typically sucrose or high-fructose corn syrup.
These dissolved sugar molecules disrupt the ability of water molecules to align into the crystalline structure of ice. To overcome this interference and form a solid lattice, the solution must be cooled below the freezing point of pure water. The more concentrated the solute, the greater the depression of the freezing point.
Regular sodas, with their high sugar concentration, often freeze around \(28^\circ\text{F}\) to \(30^\circ\text{F}\) (about \(-2^\circ\text{C}\) to \(-1^\circ\text{C}\)). Diet sodas use artificial sweeteners, which contribute far fewer dissolved particles. Since they contain fewer solutes, diet sodas freeze at a temperature much closer to pure water, sometimes only a fraction of a degree below \(32^\circ\text{F}\).
The Influence of Carbonation and Container Pressure
The dissolved carbon dioxide (\(\text{CO}_2\)) gas that creates the fizz also acts as a solute, contributing to Freezing Point Depression. Although less significant than sugar, carbonation helps slightly lower the freezing temperature. The \(\text{CO}_2\) is injected and kept dissolved under high pressure within the sealed container.
This pressure allows a high concentration of \(\text{CO}_2\) to remain in the liquid phase. When a supercooled soda (chilled below its freezing point but not yet solid) is opened, the internal pressure is immediately released. This sudden drop causes the \(\text{CO}_2\) to rapidly come out of solution, forming bubbles.
These rapidly forming gas bubbles act as nucleation sites where ice crystals quickly begin to form. This leads to flash freezing, where the liquid instantly turns into a slushy solid upon opening. The freezing point of the liquid rises slightly when the \(\text{CO}_2\) escapes, making it susceptible to rapid solidification.
Practical Effects of Freezing Soda
Allowing soda to fully freeze in its container leads to significant practical problems due to water’s unique physical properties. Water expands in volume by about nine percent when it changes from a liquid to a solid state. Since soda is mostly water, this expansion exerts immense force on the container walls.
Sealed aluminum cans and glass bottles are not designed to withstand this internal pressure. This frequently results in the container rupturing or exploding, which creates a sticky mess and poses a physical hazard.
Freezing also degrades the quality of the beverage, even if the container remains intact. The process separates the components, causing water to freeze first and concentrating the sugar and flavorings into a syrupy liquid. When thawed, the original homogeneous mixture is not fully restored, resulting in a less palatable taste. Furthermore, dissolved \(\text{CO}_2\) is forced out of solution during freezing, leaving the thawed drink noticeably flat.